1. Field of the Invention
This invention relates to a perpendicular magnetic recording medium (PRM), more particularly to a perpendicular magnetic recording medium having an antiferromagnetic layer and a perpendicular magnetic recording layer formed on the antiferromagnetic layer and exchange-coupled to the antiferromagnetic layer.
2. Description of the Related Art
As technology advances, approaches have been made to increase the recording density of a magnetic recording medium. However, an increase in the recording density may cause superparamagnetic problem, i.e., the magnetic recording layer has an unstable magnetic moment, to occur.
The superparamagnetic problem can be alleviated by using a perpendicular magnetic recording medium. The perpendicular magnetic recording medium includes a magnetic recording layer with magnetic moments directed to a direction normal to the magnetic recording layer so that the stability of the magnetic moments and the magnetic anisotropic energy (Ku) of the magnetic recording layer can be increased.
Referring to FIG. 1, U.S. Patent Application Pub. No. 2008/0166596 A1 discloses a perpendicular magnetic recording medium (PRM) 1 that includes a substrate 11, an adhesion layer 12 formed on the substrate 11, a soft magnetic underlayer (SMUL) 13 formed on the adhesion layer 12, a Re-based alloy interlayer 14, such as ReMn alloy, formed on the SMUL 13, a perpendicular hard magnetic layer 15 formed on the Re-based alloy interlayer 14, a protective overcoat 16 formed on the perpendicular hard magnetic layer 15, and a lubricant topcoat 17 formed on the protective overcoat 16. The Re-based alloy interlayer 14 functions to refine the grain size of the perpendicular hard magnetic layer 15 and to enable the perpendicular hard magnetic layer 15 to have a desired orientation texture, i.e., (0002) orientation texture, along a direction normal to the perpendicular hard magnetic layer 15. For instance, when the Re-based alloy interlayer 14 is made from ReMn alloy, since Mn atoms of the ReMn alloy have a solubility lower than 6 at %, an excessive amount of Mn present in the ReMn alloy will cause segregation of Mn atoms to occur at the grain boundaries of the Re crystal grains, which results in grain refinement of the Re-based alloy interlayer 14, which, in turn, results in grain refinement of the perpendicular hard magnetic layer 15 and an increase in the recording density of the PRM 1. In addition, the magnetic anisotropy energy (Ku) and coercive field (Hc) of the perpendicular hard magnetic layer 15 can be increased by virtue of the (0002) orientation texture possessed by the perpendicular hard magnetic layer 15.
Referring to FIG. 2, U.S. Patent Application Pub. No. 2008/0085426 A1 discloses an exchange coupled composite perpendicular magnetic recording medium (ECCPRM) 2 that includes a substrate 21, a soft magnetic lining layer 22 formed on the substrate 21, a seed layer 23 formed on the soft magnetic lining layer 22, a foundation layer 24 formed on the seed layer 23, a Ru-based alloy middle layer 25, such as RuMn, having a hcp crystal structure and formed on the foundation layer 24, a recording layer 26 formed on the Ru-based alloy middle layer 25, a protective layer 27 formed on the recording layer 26, and a lubricating layer 28 formed on the protective layer 27. The recording layer 26 includes a first recording film 261, an exchange-coupling-strength control film 262 made from Ru-based alloy, such as RuMn, an auxiliary recording film 263, and a second recording film 264 from bottom to top in this sequence so as to form an exchange-coupling in ferromagnetism between the first recording film 261 and the auxiliary recording film 263 and to decrease the switching field (Hs) of the ECCPRM 2. It is noted that the purpose of including the Ru-based (RuMn) alloy middle layer 25 in the ECCPRM 2 is to provide a function similar to the Re-based (ReMn) alloy interlayer 14 in the aforementioned PRM 1 so that the (0002) orientation texture, the magnetic anisotropy energy (Ku), and the coercive field (Hc) of the recording layer 26 can be improved.
However, there still remains a need in the art to provide a perpendicular magnetic recording medium having a magnetic recording layer which exhibits superior orientation texture, Ku, and Hc.